When a body of aluminum is melted in a furnace for purposes of casting or the like, dross forms on the surface of the molten aluminum which must be periodically removed, for example by skimming or similar operation. The removed dross contains substantial amounts of free aluminum as well as aluminum oxides, such as bauxite, and certain other metals and metal salts, such as magnesium, manganese, and lithium depending on the nature of the aluminum or aluminum alloy being treated.
It is recognized in the industry that for economical reasons it is critical to recover in usable form the free aluminum, aluminum oxide, and other by-product metals from the dross. It is also recognized, however, that the recovery of these materials from dross is difficult due, inter alia, to the nature of the dross and the reactivity of aluminum. In a typical recovery process the dross is normally melted at high temperatures in a furnace. However, at elevated temperatures the dross, particularly the free aluminum in the dross, is easily susceptible to oxidation and, moreover, commonly tends to ignite and burn in the presence of air. The burning of the aluminum can decrease substantially the amount of aluminum recovered. To solve the problems associated with treating dross and improve the efficiency of aluminum recovery, it has been proposed to heat the dross in an induction furnace in the presence of a salt flux. See, for example, McLeod et al, U.S. Pat. No. 3,676,105.
The art also recognizes that similar problems are encountered when recovering free aluminum from aluminum scrap such as aluminum cans or other scrap material. See, for example, Bamji et al, U.S. Pat. No. 4,571,258.
It has also been suggested in the prior art to recover aluminum metal in the gaseous state by breaking down aluminum salts at temperatures of at least 2500.degree.to 5500.degree. C. using plasma energy from a plasma arc torch. In this operation the need to protect against the problems associated with oxidation and burning of the aluminum are recognized. See, for example, Othmer, U.S. Patent No. 3,938,988.
The use of a plasma jet generator has also been suggested for reducing various metal oxides, including aluminum oxides, which melt at a temperature below the boiling point of the metal to be recovered. It is stated that the gas which is energized in the plasma jet generator is an inert gas such as helium, neon, xenon, krypton, or nitrogen.
Accordingly, there is a substantial need in the industry for an improved process for recovering free aluminum, aluminum compounds such as the aluminum oxides, and by-product metals from aluminum dross and from aluminum scrap. It is particularly desirable that such process be ecologically safe and not contaminate the environment.